1. Field of the Invention
The invention relates, in general, to angle measuring devices, and more particularly, to apparatus for marking a reference line at a predetermined angle from an established base line.
2. Description of the Prior Art
Craftsmen, such as carpenters, find it necessary to mark a reference line (normally 90.degree.) from an established base line. The craftsmen normally utilize the Pythagorean Theorem formulation of: EQU c.sup.2 =a.sup.2 +b.sup.2
to determine a right angle.
For example, the craftsmen measures a distance of four feet along an established base line from a given point and then measures a distance of three feet along a reference line extending from said point at approximately a right angle. To determine if the right angle has been correctly formed, the ends of the lines along the base line and the reference line, when connected, should equal five feet. If the distance is not five feet he must then go back and re-execute the reference line to correct for the error. Such techniques have been found to be time consuming, inaccurate and difficult for the craftsman to calculate when the distances involved are more or less than surfaces where a 3-4-5 triange can be constructed.
Other devices for forming right angles are also well known but have been found to be bulky, difficult to read, or not disposed for rapid reading.
One such device is disclosed in U.S. Pat. No. 4,381,607 wherein the tool includes an elongated member from which angle lines or cords are each adapted to extend a predetermined distance such that the intersecting terminal ends of the cords, in combination with the member, form a triangle having sides of known length. In as much as the length of the triangle sides are known, the angles included thereby are also known such that a chalk line connected to the member may be utilized to establish a reference line at a known angular disposition to the member.
In U.S. Pat. No. 2,758,380 three corner pieces are interconnected together by non-flexible stretchable members to form a right angle triangle when the flexible members are in a taut condition.
In U.S. Pat. No. 2,683,933 a pair of members are connected together so that they assume various angular relationships. A flexible member interconnects the ends of the two members so that the combination can simulate respective legs of a triangle, the connection being such that the length of any triangle leg and the angular relationship of the legs may be readily changed.
Other known devices include U.S. Pat. Nos. 3,459,429; 3,885,314; 3,514,863; and 3,269,015.
While certain of the above-mentioned devices may be utilized to determine a right angle with respect to a reference line, none of these devices are simple, compact and yet readily available for large measurements and are easily read by an unskilled craftsman.
The manner in which the invention addresses the disadvantages of the prior art to provide a novel and highly advantageous apparatus for marking a reference line on a working surface at a predetermined angle or disposition from an established line will be understood as this description proceeds.